title: Two rotary motors in F-ATP synthase are elastically coupled by a flexible rotor and a stiff stator stalk.
abstract: ATP is synthesized by ATP synthase (F(O)F(1)-ATPase). Its rotary electromotor (F(O)) translocates protons (in some organisms sodium cations) and generates torque to drive the rotary chemical generator (F(1)). Elastic power transmission between F(O) and F(1) is essential for smoothing the cooperation of these stepping motors, thereby increasing their kinetic efficiency. A particularly compliant elastic domain is located on the central rotor (c(10-15)/ε/γ), right between the two sites of torque generation and consumption. The hinge on the active lever on subunit β adds further compliance. It is under contention whether or not the peripheral stalk (and the "stator" as a whole) also serves as elastic buffer. In the enzyme from Escherichia coli, the most extended component of the stalk is the homodimer b(2), a right-handed α-helical coiled coil. By fluctuation analysis we determined the spring constant of the stator in response to twisting and bending, and compared wild-type with b-mutant enzymes. In both deformation modes, the stator was very stiff in the wild type. It was more compliant if b was elongated by 11 amino acid residues. Substitution of three consecutive residues in b by glycine, expected to destabilize its α-helical structure, further reduced the stiffness against bending deformation. In any case, the stator was at least 10-fold stiffer than the rotor, and the enzyme retained its proton-coupled activity.
authors.affiliation: Department of Biophysics, University of Osnabrück, 49069 Osnabrück, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Wächter
authors.forename: Yumin
authors.initials: Y
authors.lastname: Bi
authors.forename: Stanley D
authors.initials: SD
authors.lastname: Dunn
authors.forename: Brian D
authors.initials: BD
authors.lastname: Cain
authors.forename: Hendrik
authors.initials: H
authors.lastname: Sielaff
authors.forename: Frank
authors.initials: F
authors.lastname: Wintermann
authors.forename: Siegfried
authors.initials: S
authors.lastname: Engelbrecht
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Junge
mesh_terms: D000595:Amino Acid Sequence; D004548:Elasticity; D004926:Escherichia coli / Q000201:enzymology; D008280:Magnetics; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D020409:Molecular Motor Proteins; D006180:Proton-Translocating ATPases